Why Axis yards constrained a German carrier fleet

Could Axis cooperation and synthetic-oil technology have delivered German carriers before the invasion of the Soviet Union?

Not easily; yard capacity, construction time, delivery routes, and a British counter-programme remain decisive constraints.

Japan could share knowledge, but building German carriers there would consume Japanese capacity and leave the problem of delivering the completed ships to Europe. Germany itself had too few suitable building positions, while Italy's partly available yards were also occupied with the Littorio programme. Any Italian construction would have to begin early, and Italy would probably demand carriers of its own. Britain would observe the programme and respond with faster production of larger armoured carriers, more aircraft per ship, and perhaps an earlier Unicorn sister. Alliance technology transfer cannot overcome geography, slipway capacity, and an opponent's reaction.